Weather Window | Winter wrap up

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TAHOE — The 2012 water year for the Sierra Nevada won’t officially end until Sept. 30, but for all intents and purposes our lackluster winter is over. It should be no surprise by now that precipitation last season was significantly below normal. Despite an impressive battery of storms in March that dumped up to 9 feet of snow on Tahoe resorts, followed by a wet April, it would have taken something closer to the “Miracle March” of 1991 to raise this year’s disappointing snowpack values to near normal.

The final snow survey of the season indicated an anemic snowpack averaging about 40 percent of normal for early May, varying from 77 percent in the north, 35 percent in the central region, all the way to 20 percent in the Southern Sierra. The recent measurements were in stark contrast to 2011 when the Sierra was still buried under a snowpack 190 percent of normal on May 1. Fortunately, that huge, late season snowpack a year ago will help mitigate this year’s paltry water supply because California’s major reservoirs are close to or exceeding capacity. With the crucial exception of certain farming districts, no water restrictions are anticipated for the 25 million Californians who rely on the Sierra snowmelt. Locally, reservoir storage in the Truckee River Basin stood at 128 percent of average on May 1.

Ironically, a little more than one year after California Governor Jerry Brown declared the end of a three-year drought in March 2011, the state’s driest winter in 50 or 60 years has desiccated the landscape and more than 60 percent of the Golden State is back to abnormally dry or severe drought status. And it wasn’t just the West Coast that suffered last winter. The United States ski industry was seriously impacted in 2011 by lack of snow combined with one of the mildest seasons on record that hampered snowmaking. At Lake Tahoe, skier visits at Northstar and Heavenly were down 24 percent compared to 2011. Skiing conditions were fine in March and April, but the magic came too late to save a busted season. A lack of snow during the all-important New Year holidays and negative publicity about Tahoe conditions took its toll. With such a poor start, there was no way regional resorts would be able to compete with the epic 2011 winter, in my opinion the most hyped ski season in modern times.

At the Central Sierra Snow Laboratory, station manager Randall Osterhuber reported that as of May 3, 322 inches of snow had been measured so far. That total of 26.8 feet puts winter 2012 at the 50th least snowiest in 66 years of record keeping. Precipitation-wise, the 42-plus inches of rain and melted snowfall rank 2012 as the 55th driest since 1946. Not too bad when you consider that at the beginning of March, 2012 was among the top 10 driest seasons in well over a century. After such a bad start, last winter could have turned out much worse.

Looking ahead to next ski season, the La Nina conditions of 2011 and 2012 have dissipated and transitioned to ENSO-neutral conditions (El Nino Southern Oscillation). Other than possible temperature anomalies, ENSO conditions in the Pacific Ocean usually have little effect during the dry summer months from May into October. In their latest diagnostic discussion released May 3, NOAA’s Climate Prediction Center stated that La Nina conditions are unlikely to re-develop later this year, and that half their computer models predict the onset of El Nino and warming sea surface temperatures this summer.

Moving forward into the 2013 ski season, however, NOAA’s latest ENSO update indicated there is considerable forecast uncertainty due to their inability to predict “whether warmer sea surface temperatures (SST) will result in the ocean-atmosphere coupling required for a sustained El Nino event.” In other words, will the warmer ocean temperatures expected this upcoming winter translate into an enhanced, moisture-laden subtropical jet stream often associated with El Nino conditions? That classic El Nino-influenced storm pattern tends to soak Southern California and the Desert Southwest. Historically, El Nino events trend wetter than normal in the Central Sierra, a plus for Tahoe resorts.

Five of the past seven Sierra winters have been under the influence of La Nina, conditions that often bring a drier and warmer winter to Southern California. That temperature/precipitation signal is less pronounced in Northern California. (The epic winter of 2011 was a major exception to that trend up and down the state.) NOAA can’t predict what’s in store for 2013, but regardless of whether ENSO conditions are positive, negative or neutral next winter, even a normal season of precipitation will be better than last year and should offer plenty of white stuff for locals and visitors alike.

— Tahoe weather historian Mark McLaughlin is a nationally published author and professional speaker. His award-winning books are available at local stores or at www.thestormking.com. You can reach him at mark@thestormking.com